For the purpose of correcting presbyopia for example, it is widely known to prescribe multifocal contact lenses, such as bifocal lenses having multiple diopter power regions, and specifically a distance region provided as a first diopter power region and a near region provided as a second diopter power region having more positive additional diopter power than that of the distance region.
As one multifocal contact lens of this kind, the multifocal contact lens disclosed for example in Patent Document 1 (JP-A 61-272717) has a distance region and a near region formed with concentric circular shape centered on the geometric center of the lens. However, it is known that the center of the pupil is biased slightly towards the nasal side from the center of the cornea. For this reason, it is difficult for contact lenses with a shape like that disclosed in Patent Document 1, in which the distance region and the near region are formed with concentric circular shapes from the geometric center of the lens on the assumption that the lens geometric center is aligned with the center of the pupil, to maintain the desired positional relationship between the pupil and the two regions during actual wear. As a result, neither distance vision nor near vision was corrected effectively.
In view of this, the Applicant proposed in Patent Document 2 (JP-A 6-289329), a multifocal contact lens in which the near region is biased towards the nasal side from the lens geometric center. This successfully reflects the fact that, in the case of near vision, the axis of vision lies closer towards the nasal side, making it possible to provide effective correction of both near vision and distance vision owing to the resultant aligning of the lens optical axis with the axis of vision.
However, with a multifocal contact lens such as that disclosed in Patent Document 2, due to the fact that for some wearers the near region is biased not only in the horizontal direction but also in the vertical direction, it was necessary to provide separate lenses for the right eye and for the left eye. This requires additional specifications for left and right. For this reason, in the case of a made-to-stock production system, it would be necessary to have extensive inventory available, potentially leading to both increased production costs and administrative costs. Also, left and right lenses need to be handled separately, even for wearers having the same specifications for both the left and right eye.    Patent Document 1: JP-A 61-272717    Patent Document 2: JP-A 6-289329